Feed which undergoes cryogenic rectification must be first cleaned of high boiling impurities because such impurities will freeze at the cryogenic temperatures thus burdening the separation.
In the cryogenic separation of feed air for example, the feed air is cleaned of high boiling impurities such as water vapor, carbon dioxide and hydrocarbons by passage through a prepurifier such as a molecular sieve adsorption unit.
The prepurification of the feed is carried out more efficiently if the feed is chilled prior to prepurification. Chilling the feed condenses out water, which reduces the quantity of water adsorbed by the prepurifer. This reduces the quantity of the adsorbent required and also reduces the regeneration energy requirements.
Generally, the chilling of the feed prior to the prepurificaton is carried out using a mechanical chiller or other energy consuming piece of equipment to chill or refrigerate the feed. This contributes significantly to the operating costs of the cryogenic rectification inasmuch as the entire feed must undergo the chilling.
Accordingly, it is an object of this invention to provide a cryogenic rectification system wherein cooling or chilling the feed is carried out in a more efficient manner compared with conventional cryogenic rectification systems.